A degree of relief for state conservation officials: Evidence of invasive bighead and silver carp in Minnesota's lowest section of the Mississippi River is almost nil.

Out of 500 samples taken for testing in August from three pools in the river along the state's southeastern border, one indicated "only a small presence" of evidence of invasive carp DNA, the Minnesota Department of Natural Resources (DNR) announced Monday.

"The lone positive bighead result appears to support historical, physical catch evidence of low numbers of invasive carp in this stretch of the Mississippi River," said Nick Frohnauer, the DNR's invasive fish coordinator. "Individual captures of adult bighead and silver carp have occurred since 2008, but none were captured in these pools in 2014."

The positive sample detected environmental DNA (eDNA) and came from the river near Winona. The presence of eDNA does not provide physical proof of the existence of live or dead carp, but it indicates genetic material that may have come from a live carp or transported to the place of detection on a boat or by other means.

This is the first time samples were collected in these three pools of the river, two near Winona and one just north of the Iowa border. The U.S. Fish and Wildlife Service, in consultation with the DNR, conducted the sampling, which was analyzed last month. Officials said they intend to take more samples in these same spots and in pools farther north.

In August 2013, a silver carp was found dead at the base of the Mississippi River dam at Winona, a discovery that was at that time the farthest north the species had been detected. Silver carp are notoriously known for dangerously flying out of the water to the dismay of boaters.

In July 2014, two invasive carp, a 40-pound bighead and a 20-pound silver, were netted in Cottage Grove, marking their northernmost known migration to date along the Mississippi River. The capture of the two was the first evidence that bighead carp had advanced past the mouth of the St. Croix River near Prescott, Wis.

Asian carp were imported to the United States in the 1970s to clean fish ponds in the South. During floods, they escaped into the wild and have been migrating north along the Mississippi and its tributaries ever since. They have advanced to within a few dozen miles of Lake Michigan in the Illinois River, which connects with a shipping canal and other waters that reach the great lake bordering Wisconsin, Michigan and Illinois.

Paul Walsh • 612-673-4482